Multi-disciplinary three-dimensional representations of building designs are available in BIM. However, thermal analysis often remains a manual task due to disparities in modelling: In IFC, buildings are decomposed into sets of elements with individual solid volumes. Thermal analysis requires interfaces between pairs of adjacent spaces. In this work, we present an end-to-end solution for thermal analysis on IFC building models. We derive thin-walled thermal interfaces from architectural building models using voxelization. Neighboring spaces (separated by wall volumes in IFC) are touching after aligning to the voxel grid. The resulting mesh is converted into OSM files for OpenStudio/EnergyPlus. This paper provides an implementation, discussion and initial validation. The algorithm depends on a minimal amount of information and favors robustness over accuracy, algorithms on voxels are robust. It is suitable for early design feedback and partial or imperfect scan2bim models.@en